In a cellular mobile communication system and the like, such a system wherein an array antenna receiver device composed of a plurality of antenna elements having high correlations one another is used, whereby a reception directivity pattern is formed such that a reception gain increases with respect to an arrival direction of a desired signal, while a reception gain decreases with respect to interferences due to an interference or a delay wave from other users is heretofore studied with an intention of high speed/high quality of signals and increase in a capacity of subscribers.
Incidentally, in an array antenna receiving device having a plurality of radio receiving parts of antennas, generally, amplitude and phase variations in the radio receiving parts of the antennas connected to antenna elements, respectively, are independently varied every second. Accordingly, it is necessary for compensating such variations of phase and amplitude at the time of forming a reception directivity pattern, and such operation is called by the name of calibration.
As a conventional calibration method, there is, for example, a manner described in Japanese Patent Application Laid-open No. 11-46180 (Calibration apparatus for array antenna receiver device) wherein a known calibration signal is input to each radio receiving part connected to each antenna element, a demodulated result of the calibration signal is used to compensate phase (delay) and amplitude variations in each radio receiving part which varies independently every second.
FIG. 1 is a block diagram illustrating an array antenna receiver device for exemplifying a calibration described in the above patent application laid-open official gazette. The array antenna receiver device is composed of an array antenna 901, multiplexing circuits 9031 to 903N, a radio receiving part 9041 of an antenna 1 to a radio receiving part 904N of an antenna N corresponding to antenna elements, respectively, a signal processing part 9051 of a user 1 to a signal processing part 905M of a user M corresponding to the number of users, a calibration signal generating part 906, a calibration radio transmitting part 907, a power level variable part 908, N distributors 909, and a calibration signal processing part 910 wherein N of the N distributors corresponds to the number of antenna elements (multiplexing circuits).
The array antenna 901 is composed of the N antenna elements 9021 to 902N. The N antenna elements 9021 to 902N are closely disposed so as to have correlations among reception signals of the respective antenna elements, wherein desired signals are multiplexed with a plurality of interference signals are received. For the sake of discriminating a usual diversity construction, N of the number of antenna elements is to be three or more.
To the multiplexing circuits 9031 to 903N, N outputs of the N distributors 909 and outputs of the antenna elements 9021 to 902N are input to perform multiplexing in a radio transmission band, and the results are output to the radio receiving part 9041 of the antenna 1 to the radio receiving part 904N of the antenna N. A multiplexing method is not limited, but there is, for example, code multiplexing.
Each of the radio receiving part 9041 of the antenna 1 to the radio receiving part 904N of the antenna N is composed of devices such as a low noise amplifier, a band pass filter, a mixer, synthesizers, an AGC (Auto Gain Controller), a demodulator, a low pass filter, and an analog-to-digital converter (ADC) An explanation will be made herein upon the radio receiving part 904N of the antenna N as an example. To the radio receiving part 904N of the antenna N, an output of the multiplexing circuit 903N is input to perform amplification of an input signal, a frequency conversion from a radio transmission band to a base band, demodulation, an analog-to-digital conversion and the like, and the results are output to the signal processing part 9051 of the user 1 to the signal processing part 905M of the user M and the calibration signal processing part 910.
To the calibration signal processing part 910, outputs of the radio receiving part 9041 of the antenna 1 to the radio receiving part 904N of the antenna N are input to extract calibration signals in input signals thereby to detect phase/amplitude information of the antenna 1 to phase/amplitude information of the antenna N, and the results are output to the signal processing part 9051 of the user 1 to the signal processing part 905M of the user M. It is to be noted that a calibration signal multiplexed with an input signal is extractable.
To the signal processing part 9051 of a user 1 to a signal processing part 905M of a user M, outputs of the radio receiving part 9041 of the antenna 1 to the radio receiving part 904N of the antenna N and the phase/amplitude information of the antenna 1 to the phase/amplitude information of the antenna N being outputs from the calibration signal processing part 910 are input. Then, a reception directivity pattern is formed in such that a reception gain increases with respect to a user signal arrival direction in each user, while a reception gain decreases with respect to interferences from other users or an interference due to a delay wave while compensating outputs from the radio receiving part 9041 of the antenna 1 to the radio receiving part 904N of the antenna N by the use of the phase/amplitude information of the antenna 1 to the phase/amplitude information of the antenna N, and a demodulation signal of the user 1 to a demodulating signal of the user M received by the reception directivity pattern are output.
The calibration signal generating part 906 produces a calibration signal in a base band, and the resulting calibration signal is output to the calibration radio transmitting part 907. To the calibration radio transmitting part 907, a calibration signal in a base band being an output of the calibration signal generator 906 is input to perform a digital-to-analog conversion, a frequency conversion from a base band to a radio transmission band and the like, and the results are output to the power level variable part 908.
To the power level variable part 908, a calibration signal in the same frequency band as that of a reception signal derived from the antenna elements 9021 to 902N being an output of the calibration radio transmitting part 907 is input, and the results are output to the N distributors 909 at an arbitrary electric power level. The N distributors N-distribute calibration signals in a radio transmission band being outputs of the power level variable part, and the results are output to the N multiplexing circuits 9031 to 903N, respectively.
Each of signals received by the N antenna elements 9021 to 902N contains a desired (user) signal component, an interference signal component, and thermal noises. Moreover, a multipath component exists, respectively, in the desired signal component and the interference signal component, and these signal components arrived usually from different directions.
The array antenna receiver device of FIG. 1 discriminates respective signal components of different arrival directions with the use of phase/amplitude information of the respective signals received by the N antenna elements 9021 to 902N to form a reception directivity pattern.
In these circumstances, there is a case when phase/amplitude variations appear inside the respective radio receiving parts dependent upon a constructional device of the radio receiving part 9041 of the antenna 1 to the radio receiving part 904N of the antenna N. As a result, different information from primary phase/amplitude information of the respective signals received by the antenna elements 9021 to 902N is given to the signal processing part 9051 of the user 1 to the signal processing part 905M of the user M, so that it becomes impossible to discriminate correctly the respective signal components, and thus, an ideal reception directivity pattern cannot be formed.
Accordingly, a reception signal is multiplexed with a calibration signal in the same frequency band as that of the reception signal received by the antenna elements 9021 to 902N to detect phase/amplitude information of a calibration signal extracted from the respective outputs of the radio receiving part 9041 of the antenna 1 to the radio receiving part 904N of the antenna N in the calibration signal processing part 910, whereby phase/amplitude information given by the signal processing part 9051 of the user 1 to the signal processing part 905M of the user M is corrected.
When multiplexed with a calibration signal as described above, a calibration becomes possible even in case of working the array antenna receiver device. Namely, a calibration signal is in a state where it is multiplexed with a reception signal from a mobile phone, so that only a calibration signal component can be extracted. An example of such case as described above includes code multiplexing.
Non-linear circuits (particularly, an AGC) contained in the radio receiving part 9041 of the antenna 1 to the radio receiving part 904N of the antenna N exhibit different manners of phase/amplitude variations dependent on a reception electric power level. Accordingly, a calibration signal of each output of the radio receiving part 9041 of the antenna 1 to the radio receiving part 904N of the antenna N is extracted while changing a calibration signal power level with the power level variable circuit 908 to detect phase/amplitude information, whereby a calibration amount to be applied to phase/amplitude information given to the signal processing part 9051 of the user 1 to the signal processing part 905M of the user M in each calibration signal power level is determined.
The array antenna receiver device having such calibration means as described above can correct the phase/amplitude information given to the signal processing part 9051 of the user 1 to the signal processing part 905M of the user M, even in a case where phase/amplitude variations appear inside the radio receiving part 9041 of the antenna 1 to the radio receiving part 904N of the antenna N at the time of application thereof. Furthermore, it is possible to achieve a high precision in response to a power level of a reception signal. Thus, according to the array antenna receiver device of FIG. 1, respective signal components having different arrival directions one another are discriminated with the use of phase/amplitude information of respective signals received by the N antenna elements 9021 to 902N, so that an ideal reception directivity pattern can be formed.
However, the above-mentioned conventional array antenna receiver device involves the following problems. Namely, a first problem is in that the optimum calibration cannot be applied to all the reception branches in the case when a calibration is conducted at the time of application of the system. The reason of which is in that a magnitude of a reception signal input from each antenna element (a communication signal from a mobile phone, noises, an interference signal from other systems) exhibit a remarkable dispersion as a result of being affected adversely by fading and the like, so that a ratio of a calibration signal input to each reception branch in a constant equal electric power and a reception signal being an interference signal from an antenna element differs remarkably with each other.
Moreover, a second problem is in that a calibration of a high precision cannot be achieved in the case when a trouble occurs in a certain reception branch. The reason of which is in that the conventional array antenna receiver device is not provided with a means for judging signal quality of a calibration signal and a means for excluding the reception branch in which a trouble occurs.
A third problem is in that reception sensitivity of the array antenna receiver device deteriorates as a result of implementing a calibration in case of working the system. The reason of which is in that a calibration signal is a mere interference signal for a communication signal (desired wave) with a mobile phone and which is input from an array antenna, besides, particularly, when a calibration signal of a high level is input, an interference signal component increases.
A fourth problem is in that when a calibration is conducted at the time of working the system, the number of users in the system decreases. The reason of which is in that a calibration signal in question becomes an interference wave to deteriorate a ratio of a user signal from a mobile phone with respect to such interference signal, so that a transmission electric power in the mobile phone increases for demodulating the user signal with desired signal quality in its radio base station installation.